Abstract <p>Theoretical models of elasticity and thermal conductivity have been developed for a polycrystal with imperfect grain boundaries and residual porosity. Based on the analysis of research data by these models, a quantitative estimate has been obtained for the thermal conductivity and elasticity of grain boundaries in polycrystalline cubic boron nitride, and the effect of the sintering temperature on them was studied. A strong dependence of macroscopic thermoelastic properties of a polycrystal on the state and properties of grain boundaries enables the application of the latter as a criterion of structural perfection in a polycrystal.</p>